For 45 introduced Pinaceae species planted 100 years ago on an island dominated by native forests in Patagonia, and for the subset of 24 species naturalized on this island, we evaluated the relationship between traits (seed mass, maximum height, wood density, juvenile period and interval between large seed crops) and invasion incidence (whether a species has become invasive or not) or extent (number of invaded transects across the study area).

Site Description

We conducted our study on Isla Victoria (40° 57´ S, 71° 33´ W; ca. 3710 ha), an island in Lake Nahuel Huapi, Parque Nacional Nahuel Huapi (Argentina). Annual precipitation is 1300 mm and mean annual temperature is 10.1°C. Soils are classified as andisols (volcanic soils) with low phosphorus levels (Satti et al. 2007). The island is mostly forested, dominated by either Nothofagus dombeyi or Austrocedrus chilensis. Between 1910 and 1940, 45 non-native Pinaceae species were planted in large numbers in two major areas of the island (see Simberloff et al. 2002 for more detail):

a) Puerto Anchorena (ca. 150 ha): all 45 introduced Pinaceae species were planted in this area.

b) Puerto Pampa (ca. 34 ha): only 3 Pinaceae species were planted here (Pinus contorta, P. sylvestris, and Pseudotsuga menziesii).

For most species, more than 1,000 individuals were planted. After 1940 no new species were introduced. Of these 45 initially introduced species, 24 have become naturalized, producing offspring only near the original plantations.

Sampling Procedure

Pinaceae traits

For the 45 Pinaceae species introduced to the island we used global open access databases to gather data on maximum height registered across the world (“The Gymnosperm Database”; https://www.conifers.org), wood density (Chave et al. 2009), and seed mass (Liu et al. 2019); https://ser-sid.org/). We also wanted to assess if the Z score, used to predict invasions in treeless ecosystems, was also useful to predict Pinaceae invasions in forests. However, instead of using the same index we focused on the traits that were used to calculate the Z score: seed mass, juvenile period, and interval between large seed crops (Rejmánek and Richardson 1996, Rejmánek et al. 2005), and we gathered data on these traits from the literature.

For the 24 Pinaceae species naturalized on the island we measured the maximum height of the individuals from the original plantations (approximately 100 years old) by identifying the tallest 5 individuals and measuring their height using a clinometer (Suunto PM-5). Further, we measured wood density for these five individuals of each species using a core borer (Haglöf Sweden 3-thread increment borer 16”L by 0.200”). For each individual we extracted a sample that extended from the center to the bark. To obtain the sample fresh volume we measured its length with a measuring tape and measured its width at three different points (to get an average) with an electronic caliper (Chave 2006). Each core sample was then oven dried at 60° C for 72 hours and weighed with a precision scale (0.001 g) to obtain its dry weight. To obtain the sample wood density (g/cm³), we divided the sample dry mass (g) by its volume (cm³). For seed mass, we were unable to obtain seeds from all species on the island (for some species most reproductive trees are extremely tall with cones that are very difficult to reach), so we used values from a global database (Liu et al. 2019; https://ser-sid.org/) (seed mass is a trait with relatively low variation among individuals of the same species; McGill et al. 2006). In the case of juvenile period and interval between large seed crops we also had to gather these data from the literature because to measure them in the field would require decades.

Invasion surveys

We surveyed all invasive individuals from each introduced Pinaceae species in 2010, using transects 10 m wide and 100 m apart, extending across the whole width of the island (see [Moyano et al. 2023] for more detail). Pinaceae species are wind-dispersed, and in this region predominant winds come from the northwest. To census individuals dispersed by both predominant winds and less frequent wind directions, we built our transects in three different areas of the island:

-Northwest (upwind) of Puerto Anchorena (transects 1-11)

-Southeast (downwind) of Puerto Anchorena (transects 201-209)

-Southeast (downwind) of Puerto Pampa (transects 101-104)

References

Chave, J. 2006. Medición de densidad de madera en árboles tropicales manual de campo.

Chave, J., Coomes, D., Jansen, S., Lewis, S. L., Swenson, N. G. and Zanne, A. E. 2009. Towards a worldwide wood economics spectrum. - Ecol. Lett. 12: 351–366.

Liu, U., Cossu, T. A. and Dickie, J. B. 2019. Royal Botanic Gardens, Kew’s Seed Information Database (SID): A compilation of taxon-based biological seed characteristics or traits. - Biodivers. Inf. Sci. Stand. 3: e37030.

McGill, B. J., Enquist, B. J., Weiher, E. and Westoby, M. 2006. Rebuilding community ecology from functional traits. - Trends Ecol. Evol. 21: 178–185.

Moyano, J., Simberloff, D., Relva, M. A. and Nuñez, M. A. 2023. Increasing tree invasion on Isla Victoria: 10 years after the original “gringos en el bosque” study. - Biol. Invasions 25: 3025–3031.

Rejmánek, M. and Richardson, D. M. 1996. What attributes make some plant species more invasive? - Ecology 77: 1655–1661.

Rejmánek, M., Richardson, D. M., Higgins, S. I., Pitcairn, M. and Grotkopp, E. 2005. Ecology of invasive plants: state of the art. - SCOPE—Scientific Committee on Problems of the Environment International Councils of Scientific Unions 63: 104–162.

Satti, P., Mazzarino, M. J., Roselli, L. and Crego, P. 2007. Factors affecting soil P dynamics in temperate volcanic soils of southern Argentina. - Geoderma 139: 229–240.